Efforts are in progress to improve our ability to characterize the toxicity of chemicals to neonates relative to adults, and to explore the role of lactation in the induction of neonatal toxicity. The lactational process is evaluated as a source of exposure to chemicals secreted into milk and from the standpoint of nutritional support to the newborn. A pilot study with DDE was performed which, in addition to providing an opportunity to establish and validate various techniques, generated useful information about the capacity of this insecticide to influence various parameters of lactation, including milk production, milk composition (lactose, lipid, protein components), pup growth, and mammary gland integrity (at both the morphological and biochemical levels). Other investigations have been concerned with characterizing the secretion of the liver carcinogen, dimethylnitrosamine, into milk and measuring genetic toxicity in the neonate exposed via the milk.